NRL POST Stratocumulus Cloud Modeling Efforts

Shouping Wang, William Thompson, Tracy Hack and Yi Jin

• Research issues

Wind shear impact on the entrainment and cloud structure

Stratocumulus diurnal variation in Monterey Bay area

Evaluation and improvement of stratocumulus simulation of COAMPS

Evaluation of thermodynamic fluxes in stratocumulus

• Approaches

COAMPS-LES and COAMPS mesoscale modeling

Data analysis and comparison with model output

COAMPS real time forecast

Close collaboration with other PIs.

Surface heat, moisture, and momentum fluxes

Height

0 m

vθ

vθ

ilθ

vθ

Long wavecooling

Entrainment

Subsidence

Wind ShearDrizzle

Short waveheating

zi

Sea Spray/aerosols

Turbulence

Stratocumulus-toppedMarine Boundary Layer

''

''''''

lT

llwwv

w

qwqww

A is the total water fluxB is the liquid water fluxC is the liquid water potential temperature flux A, B, and C sum to D (the buoyancy flux 100

200

300

400

500

600

700

800

900

1000

-.050 0.0 .050-.025 .025

12 h forecast profiles of buoyancy flux components for point2.

CD

B

B DC

Hei

ght

(m)

D A B

C

Vertical Profiles of Thermodynamic Fluxes In a Stratocumulus-topped, Entraining Boundary Layer

The Wind Shear Impact on the Entrainment and Cloud Structure

Temperature Total water mixing ratio

Cloud Water

Aircraft observations on 8 July 1999 in Monterey Bay area in DECS (from Qing Wang)

u v Ltq

• Strong wind shear exists at the top of clouds due to topography and land-sea contrast

• What is the effect of the intense wind shear on the entrainment?

• How does the wind shear affect the inversion structure?

• what is the response of turbulence and cloud structure to the wind shear?

The Wind Shear Impact on the Entrainment and Cloud Structure

e f g h

j k li

Buoyancy Production (m2 s-3)

Shear Production (m2 s-3)

Radiative Heating (K h-1)

Qc (g kg-1)

Theta-L (K) Qt (g kg-1) U (m s-1) V (m s-1)

COAMPS-LES Simulation

X=30m; Z=5-20m

• The intense wind shear enhances the TKE buoyancy consumption, decreases the liquid water content, and reduces the radiative cooling near the cloud top.

Strong ShearWeak ShearNo Shear

High-Resolution X=10m; Z=5m

Strong Shear

Wind Shear Impact on the Entrainment and Cloud Structure

No Shear Weak Shear Strong Shear

Inversion top Inversion base Cloud top

• The entrainment mixing is enhanced by the wind shear;

• A separation between the cloud top and inversion top is produced;

• This separation layer thickness is proportional to the intensity of the wind shear.

• Data need: soundings, entrainment zone, surface and cloud layer turbulence and cloud microphysics.

Wind shear across the inversion significantly change the inversion layer characteristics

Inversion top and base are defined by

Cloud-top is defined by the level of the highest cloudy grid point.

2l

COAMPS-LES Simulations:

07Z29-07Z30

Diurnal Variation

7:00 AM Jul 29 – 7:00 AM Jul 30, 2007 (PDT)

Monterey Bay

Salinas Valley

Diurnal Variation

• The cloud diurnal variation is caused by the diurnal change in mesoscale vertical motion, which is produced by the topography and the land surface diurnal heating.

• Data need: Soundings (above and within PBL), surface and cloud layer turbulence and cloud microphysics during day and night if possible.

Bay Area Averaged Vertical MotionBay Area Averaged Potential

Temperature and Liquid Water

Diurnal Variation of Stratocumulus in Monterey Bay: COAMPS Simulation

Diurnal Variation

• Focus

Entrainment, PBL height, cloud water, mesoscale variability.

• Data need: Soundings (above and within PBL), surface and cloud layer turbulence and cloud microphysics

Turbulent fluxes, variances at various levels

Liquid water content, droplet number concentration, drizzle rate, SST, LW and SW fluxes

• COAMPS real time forecast (James Doyle)

originally performed for AOSN (Adaptive Ocean Sampling Network) field campaign in the vicinity of Monterey Bay; now supported by CeNCOOS (http://www.cencoos.org)

can be used for POST field program;

has three grids (27, 9, 3km) and 40 levels;

produces 48 hours forecast output presented in a NRL website

Evaluation and Improvement of COAMPS Stratocumulus Simulation

COAMPS AOSN Real-Time Forecast

• http://www.nrlmry.navy.mil/coamps-web/web/mbay

• Grid 3 (3km) output are shown

• Surface, 3D fields and cross section

• Meteograms from 12 locations

Liquid water mixing ratio

Topography and Vertical Cross Sections

10 m Wind Vectors